The invention relates to a subassembly for coding images which are available in the form of digital signals corresponding to luminosity or colour information of picture elements or pixels, which images comprise at least one moving pattern against a fixed or quasi-fixed background and are to be transmitted at a very low transmission rate and/or stored at a high data compression rate, while the said subassembly comprises, for the purpose of restoration of synthesized images, on the one hand means for constructing a base model with facets representing a so-called useful zone of the original images and on the other hand means for coding data to be transmitted and/or stored. This invention is particularly useful in a coding system for videophone images.
The invention also relates to a subassembly for decoding signals representing a sequence of images, which signals, for the purpose of their transmission through a channel at a very low transmission rate and/or their storage at a high data compression rate, have been previously subjected to a coding carried out on the one hand by means for constructing a base model with facets representing the useful zone of the said images through initial calibration of the model in this useful zone followed by updating of the information representative of the model thus calibrated by tracking of the displacement of one or more windows initially defined in characteristic zones of particular interest of the said useful zone of the images, and on the other hand by means for specific coding of the essential information resulting from the said initial calibration and updating.